If the heat shows that there is nothing wrong with the water supply, the problem may be that there is something wrong with the heating water tank. It is caused by the blockage of radiator pipe in the heater box. It may be that the antifreeze is too dirty at ordinary times or the inferior antifreeze leads to rust in the waterway of the engine block, which forms mud over time and leads to blockage.
The water temperature is very slow. When running at high speed, the water temperature is basically not high, and the driving water temperature in urban areas is still a bit. Run the high-speed thermometer directly at the bottom line. This warm air is definitely not hot. This is because the thermostat can't be closed, which leads to the direct connection between the small circulation and the large circulation of water, so the warm air is not hot. The solution is to replace the thermostat.